Are you a golden oldie? The Gold Age Power List, published on Monday by the charity WRVS, trumpeted the over-66s' contribution to society: let's hear it for Delia (70), Judi Dench (76) and David Attenborough (85). Next month the 50+ show at London's Olympia will target have-a-go bungee-jumping pensioners enjoying an apparently perpetual retirement. Baby-boomers now hitting 66, the message seems to be, never had it so good.

Those on the Gold List may be chronologically old, but their good health and success ensure that they aren't socially and culturally classed as oldies. Nor are they disadvantaged economically. Indeed what distinguishes the Goldies is financial independence: they earn enough not to be reliant on a public sector starved of cash, and whose staff are among the lowest paid and lowest status of all public health workers. It's often assumed that as we age we become more alike – a generic old person. In reality class-based inequalities become even more apparent.

But while we may, as this week's Big Issue suggests, be "Fabulous After 50", we can't all be Helen Mirrens or Susan Sarandons, and the punitive ideology of choice and responsibility obscures the fact that old age is when a lifetime of low pay and sickness-producing work exacts its toll. Yet today, if you depend on the state and develop a chronic illness that needs professional care, then you've surrendered to old age: you deserve our contempt and your shabby treatment. And that same contempt for neediness is played out in the low value we place on caring for the old, whether in the home or a home.

Yet both groups – the young old and the old old – have this in common: they suffer from gerontophobia, the fear of ageing and hostility to old people. The Gold Age Power List, however admirable its intention (after all Katharine Whitehorn was involved, and she's the queen of good sense), doesn't demonstrate a new acceptance of ageing and the dismantling of stereotypes, but the opposite: our profound anxiety about age.

Nothing expresses this more than the creation of the "fourth age". In order for the "third age" to be constituted as a period of adventure and personal growth for people not past it, you need a later "fourth age" into which can be corralled all those shameful souls who are. An American survey asked 50-year-olds when old age began: the average age plumped for was 79.5 years – this when the average life expectancy of Americans was 76.1. So they really do hope they die before they get old.

Sustaining this age-denial is magic thinking: that with enough Sudoku and personal training you'll manage to bypass the fourth age altogether. By creating a new stereotype out of the mobile, healthy and affluent, you demonise the immobile, sick and poor. You also foment the belief that, through discipline and self-control, the body can always be transcended. It can't.

Age-denial is a modern phenomenon. Before the 19th century, ageing was considered something that had to be endured as part of the human condition. Increasingly this has given way to a conception of old age as a problem to which there might be a scientific solution.

With it comes a moral obligation to keep yourself young and, if you want to remain free from opprobrium, young-looking. "Ageing is a treatable medical condition," argue the anti-ageing doctors. We are the "Generation Ageless", say the so-called amortals. But hubris like this doesn't dispel gerontophobia: it embodies it.

"Productive ageing" or "successful ageing" – now common concepts – supposedly result from the exercise of willpower and choice; but they presume the existence of "unproductive" and "unsuccessful" ageing. Old age today, it seems, only befalls those too powerless, poor or stupid to do something about it – the un-Botoxed masses. We're (almost) all Dorian Grays now, tasking the fourth agers with doing our ageing for us: they are old so that we don't have to be.

In failing to control the decline of their bodies, old people contravene the presumption that the human body is infinitely malleable. They are a terrible reminder of human beings' ultimate powerlessness, of the inevitability of death; and for transgressing the idea of human omnipotence they must be punished and shamed.

We also project on to the very old our own unbearable feelings of fragility and dependency. In societies where productivity is valued and independence prized, dependence has become stigmatised. This makes it harder to accept weakness or periods of incapacity – and yet you'd be a lucky soul to go your entire life without experiencing them. Denying them means that we can't work out ways of ensuring that they don't also bring loss of dignity. Accepting them and mourning what has been lost aren't incompatible with an exuberant old age. Indeed, in many ways they make it more likely.

Obviously I'm not arguing that we shouldn't sustain vital, creative and sexual lives for as long as possible, but the idea that old age can be arrested and mastered has made ageing more frightening and harder to bear. It prevents us from seeing the arc and span of human life in all its stages. It stops us from understanding that ageing, while undoubtedly a challenging stage of life (but then adolescence is hardly a bagatelle), can be a rich part of human experience.

So no, we aren't living in a golden age of ageing. When the Zimmer frame is no longer mocked as a mark of senescence, but is seen instead as a valuable aid to staying mobile, then perhaps we might.